Femoral base plate THA

ABSTRACT

A method of creating a mass-customized femoral bone base plate comprising: (i) establishing anatomical landmarks across a plurality of bone models of a statistical atlas; (ii) establishing instrument landmarks across the plurality of bone models of the statistical atlas; (iii) establishing definitions for a reference plane calculation across the plurality of bone models of the statistical atlas, where the reference plane represents a boundary of a prosthetic implant; (iv) establishing an attachment site for a mass-customized femoral bone base plate using the anatomical landmarks, the instrument landmarks, and the reference plane; and, (v) fabricating the mass-customized femoral bone base plate configured to be attached to a femur, where the attachment sites of the mass-customized femoral bone base plate are predetermined to avoid impingement with the prosthetic implant when implanted.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Nonprovisional patentapplication Ser. No. 15/663,934, filed Jul. 31, 2017, now U.S. Pat. No.10,441,362, which is a continuation of U.S. Nonprovisional patentapplication Ser. No. 15/381,031, titled “FEMORAL BASE PLATE THA,” filedDec. 15, 2016, now abandoned, and claimed the benefit of U.S.Provisional Patent Application Ser. No. 62/267,370, titled “FEMORAL BASEPLATE THA,” filed Dec. 15, 2015, the disclosure of each of which isincorporated herein by reference.

INTRODUCTION TO THE INVENTION

The present disclosure is directed to optimization of shape, placement,and screw locations for attachment of a femoral base plate that may beused with a posterior approach for total hip arthroplasty using asurgical navigation system including inertial measurement units. As willbe discussed in more detail hereafter, the shape of the femoral baseplate is taken from the mean surface curvature of a statistical atlas offemoral bones at a defined base plate attachment site. This base plateattachment site may be dependent on screw length and locations, so thatwhen placed correctly the attachment screws do not impinge on theproposed rasp and stem components.

It should be noted that Patent Cooperation Treaty applicationPCT/US14/69411, filed Dec. 9, 2014 is hereby incorporated by reference.Portions of the foregoing application are appended hereto as Appendix A.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting a proximal portion of a femur thatincludes the femoral ball and a proposed attachment site for a bone baseplate in accordance with the instant disclosure.

FIG. 2 is a partially resected femoral bone model showing placement ofthree surgical screws and the trajectory and position relative to theintramedullary canal of the femur and the boundary of the femoral stemof an orthopedic implant positioned within the intramedullary canal.

FIG. 3 is a partially resected femoral bone model showing anintramedullary canal of the femur and the boundary of the femoral stemof an orthopedic implant positioned within the intramedullary canal.

FIG. 4 is the partially resected femoral bone model of FIG. 3 shown withthe reference plane in position.

FIG. 5 is a table showing the mean, standard deviation, minimum, andmaximum distances respective screw distal ends were with respect to thereference plane using the modeling and computations in accordance withthe instant disclosure.

FIG. 6 is a chart depicting 13 impingement circumstances where the firstscrew pierced the reference plane and how far the first screws extendedbeyond the reference plane once pierced.

FIG. 7 is a chart depicting 10 impingement circumstances where thesecond screw pierced the reference plane and how far the second screwsextended beyond the reference plane once pierced.

FIG. 8 is a chart depicting 2 impingement circumstances where the thirdscrew pierced the reference plane and how far the third screws extendedbeyond the reference plane once pierced.

FIG. 9 is a diagram showing placement of the first exemplary bonereference assembly (without the IMU) on an anterior portion of a femur.

FIG. 10 is a diagram showing placement of the first exemplary bonereference assembly on an anterior portion of a femur.

FIG. 11 is a top, elevated perspective view of an exemplary femoral bonebase plate in accordance with the instant disclosure.

FIG. 12 is a bottom, subverted perspective view of the exemplary femoralbase plate of FIG. 11 .

FIG. 13 is a top view of the exemplary femoral base plate of FIG. 11 .

FIG. 14 is a right side view of an exemplary stem in accordance with theinstant disclosure.

FIG. 15 is an elevated perspective view of the stem of FIG. 14 .

FIG. 16 is a profile view of an alternate exemplary stem.

FIG. 17 is a profile view of the exemplary stem of FIG. 14 .

FIG. 18 is an elevated perspective view of a fastener in accordance withthe instant disclosure.

FIG. 19 is a bottom view of a portion of the stem of FIG. 14 .

FIG. 20 is a partial exploded view showing the fastener, femoral baseplate, and a portion of the stem prior to assembling them as a singleelement of the first exemplary bone reference assembly.

FIG. 21 is a left and right elevated perspective view of the componentsof FIG. 20 post assembly.

FIG. 22 is a diagram showing placement of the second exemplary bonereference assembly (without the IMU) on a posterior portion of a femur.

FIG. 23 is a diagram showing placement of the second exemplary bonereference assembly on a posterior portion of a femur.

FIG. 24 is a top, elevated perspective view of a second exemplaryfemoral bone base plate in accordance with the instant disclosure.

FIG. 25 is a bottom, subverted perspective view of the exemplary femoralbase plate of FIG. 24 .

FIG. 26 is a top view of the exemplary femoral base plate of FIG. 24 .

FIG. 27 is a right side view of a second exemplary stem in accordancewith the instant disclosure.

FIG. 28 is an elevated perspective view of the stem of FIG. 27 .

FIG. 29 is an elevated perspective view of a fastener in accordance withthe instant disclosure.

FIG. 30 is a left elevated perspective view of the components of thesecond exemplary bone reference assembly.

FIG. 31 is a right elevated perspective view of the components of thesecond exemplary bone reference assembly.

FIG. 32 is a bottom view of a portion of the second exemplary stem ofFIG. 27 .

FIG. 33 is a partial exploded view showing the fastener, femoral baseplate, and a portion of the stem prior to assembling them as a singleelement of the second exemplary bone reference assembly.

DETAILED DESCRIPTION

The exemplary embodiments of the present disclosure are described andillustrated below to encompass various aspects of orthopedics includingsurgical navigation aids, surgical navigation, and mass customizedinstruments to use with surgical navigation. Of course, it will beapparent to those of ordinary skill in the art that the embodimentsdiscussed below are exemplary in nature and may be reconfigured withoutdeparting from the scope and spirit of the present invention. However,for clarity and precision, the exemplary embodiments as discussed belowmay include optional steps, methods, and features that one of ordinaryskill should recognize as not being a requisite to fall within the scopeof the present invention.

As depicted in FIG. 1 , a plurality of femoral bone models 100 (that maybe in excess of 150 models, though could certainly be less) as part of astatistical atlas (where the bone models include intramedullary canal110 models) is utilized to identify a general attachment site 102 (i.e.,landmarking) for a femoral bone base plate using bone model geometry. Inother words, this attachment site 102 for the femoral bone base plate isdelineated on each femoral bone model 100 of the atlas in generally thesame bone model area across two or more of the bone models of the atlas.Based upon this location propagation, the atlas includes local geometrydata as to the dimensions (including surface profile) of the surface ofeach bone model where the femoral bone base plate attachment site 102overlaps or is otherwise bounded by. In this fashion, the bonecontacting surface of the femoral bone base plate may be established byaveraging or otherwise using the dimensions of the bone model at theattachment site 102 locations post propagating the attachment siteacross the statistical atlas.

The following series of steps are exemplary in nature and elaborate onan exemplary femoral bone base plate attachment site 102 (landmarking)methodology in the context of establishing anatomical landmarks andreferences across the bone models 100 of the statistical atlas utilized.Though not required, the following steps may be performed on each of thebone models 100 utilized as part of the statistical atlas. In exemplaryfashion, each bone model 100 utilized as part of the statistical atlasis evaluated to: (1) compute the tip of the femoral lesser trochanterpoint (LT); (2) compute the plane marking the edge of the lessertrochanter, tangent to the femoral shaft (LTEP); (3) compute the femoraloverall anatomical axis (AA); (4) compute projection of the lessertrochanter point on the femoral overall anatomical axis (PLTPAA); (5)compute projection of the lesser trochanter point on the plane markingthe edge of the lesser trochanter (PLTPLTEP); (6) compute medial-lateraldirection as a vector between PLTPAA and LT; (7) computeanterior-posterior direction as a cross product of the femoral overallanatomical axis and medial-lateral direction; and, (8) compute superiorinferior direction as the femoral overall anatomical axis direction.

With respect to FIG. 2 , the following series of steps are exemplary innature and elaborate on an exemplary femoral bone base plate attachmentsite 102 (landmarking) methodology in the context of establishinginstrument landmarks and directions across the bone models 100 of thestatistical atlas utilized. By way of example, screw locations forsecuring the femoral bone base plate to the femur and directions thescrews 104-108 will take relative to the bone are derived from a seriesof placement steps relative to appropriate anatomical landmarks. In thisfashion, the screw locations and directions are repeatable per bonemodel 100 of the statistical atlas and, accordingly, allows for commonanalysis across the statistical atlas population utilized. Though notrequired, the following steps may be performed on each of the bonemodels utilized as part of the statistical atlas. In exemplary fashion,each bone model 100 utilized as part of the statistical atlas isevaluated to: (1) compute the shifted lesser trochanter point asPLTPLTEP is shifted 1 millimeter in the medial-lateral direction(Shifted_PLTPLTEP); (2) compute the location Screw #1 (S1) 106 as theintersection of the line pointing along the anterior-posterior directionand passing through Shifted_PLTPLTEP and the femoral bone model; (3)compute the midpoint between Screw #2 104 and Screw #3 108 as thelocation of Screw #1 (S1) 106 is shifted 5 millimeters in themedial-lateral direction (MP_S2_S3); (4) compute the location of Screw#2 (S2) 108 as the closest point on the femoral bone model to theMP_S2_S3 point shifted 1 millimeter proximally in the direction of theanatomical axis; (5) compute the point of Screw #3 (S3) 104 as theclosest point on the femoral bone model to the MP_S2_S3 point shifted 1millimeter distally in the direction of the anatomical axis; (6) computethe femoral plate plane as the plane containing the screw locations forall three Screws (Screw #1 (S1) 106, Screw #2 (S2) 108, Screw #3 (S3)104); (7) compute the direction of Screw #1 (S1) 106 as the directionnormal to the femoral plate plane; and, (8) compute the direction ofScrew #2 (S2) 108 and Screw #3 (S3) 104 to be normal to the femoralplate plane plate plane after rotating the femoral plate plane 20degrees medially around the axis connecting the location of Screw #2(S2) 108 and the location of Screw #3 (S3) 104.

With respect to FIGS. 3 and 4 , the following series of steps areexemplary in nature and elaborate on an exemplary femoral bone baseplate attachment site (landmarking) methodology in the context ofestablishing definitions for reference plane 112 calculations across thebone models of the statistical atlas utilized. The reference plane 112is a plane that represents the significant boundary of the implantedcomponent with respect to the bone in question, such as a femur. Inexemplary form, the reference plane 112 is defined so that it representsthe expected component placement (femoral implant stem) plus asignificant margin of placement error to provide a conservative estimateof the outer volume boundary of the orthopedic implant component withrespect to the bone. For purposes of explanation and assessment, anyfixation screw 104-108 is identified as having a potential impingementif its placement would result in any portion of the screw passingthrough the boundary delineated by the reference plane 112. Though notrequired, the following steps may be performed on each of the bonemodels 100 utilized as part of the statistical atlas. In exemplaryfashion, each bone model 100 utilized as part of the statistical atlasis evaluated to: (1) define a reference plane 112 normal to the proximalanatomical axis and the neck axis and passing through the anatomicalaxis point (ref_temp_plane); (2) compute the reference plane 112 as aplane rotated 5 degrees (error boundary of the system) and translated 7millimeters (determined by using a 5 millimeter measurement of anaverage rasp width and 2 millimeter buffer or safe zone built in); (3)compute the distance between the terminal end of each of the threescrews (S1, S2, S3) 104-108 and the reference plane 112, as well asnoting that any screw passing through the reference plane is identifiedas having impingement. For purposes of the foregoing, the screw lengthwas set at 13 millimeters and presumed to be flush with the outersurface of the bone model post installation/fixation. And FIGS. 3 and 4depict a femoral stem prosthetic 116 being positioned partially withinthe intramedullary canal 110.

Referring to FIGS. 5-8 , evaluation of the computations anddeterminations across all of the bone models 100 utilized as part of thestatistical atlas was carried out. As depicted in FIG. 5 , a chartprovides the mean, standard deviation, minimum, and maximum dimensionsin millimeters for the distance from the terminal end of a respectivescrew 104-108 to the reference plane. The foregoing analysis wasperformed for 150 atlas bone models. As part of the computations anddeterminations, 116 of 150 bone models had no instances of impingementbetween any of the three screws and the reference plane. In theremaining 34 cases, 15 cases had impingement of the screws 104-108 withrespect to the reference plane 112. It is worth noting that thereference plane 112 is defined based on femoral geometry landmarks,which in some cases might not correlate to the boundaries of thesegmented intramedullary canal model.

The results of the computations and determinations across all of thebone models 100 utilized as part of the statistical atlas resulted in anattachment site 102 and shape of a femoral bone base plate surfaceconfigured to be adjacent the bone surface that is mass customized tofit across a range of patient femur sizes for implant sizes that vary.

With the shape of the exemplary femoral bone base plate surface andattachment site established, one may fabricate the femoral bone baseplate 200 and use the same as part of a total hip arthroplasty procedurein order to register one or more inertial measurement units 202 withrespect to a patient's femur 204 as part of a surgical navigationendeavor. As will be discussed in greater detail hereafter, theexemplary femoral bone base plate 200 works with one or more inertialmeasurement units 202 and a stem 206 to comprise a bone referenceassembly 210. In this fashion, the inertial measurement unit (IMU) 202is fastened to a bone 204 (in exemplary form, a femur) in a fixedposition and acts as a reference IMU, where this fixed position isretained throughout the surgical procedure (which may include finalimplant placement within the intramedullary canal of the femur).Reference is had to Appendix A, included herewith, that describes inmore detail the interaction between reference IMU and a second IMUmounted to a surgical tool or surgical implant as part of surgicalnavigation in order to provide information regarding the relativepositions of bone, implant, and surgical tools when direct line of sightto one or more of these objects may be absent.

As depicted in FIG. 10 , an exemplary bone reference assembly 210 for afemur 204 comprises an inertial measurement unit 202, a stem 206, and abone base plate 200 (in exemplary form, a femoral bone base plate).Though not necessarily limited to applications on an attachment site onthe anterior region of the femur, the foregoing exemplary embodiment maybe referred to as an exemplary anterior bone reference assembly 210.

As depicted in more detail in FIGS. 11-13 , the shape of the exemplaryfemoral bone base plate 200 and fixation locations are establishedmathematically and confirmed using bone models 100 from a statisticalatlas. The exemplary femoral bone base plate 200 includes a distal, bonecontacting surface 214 having a topography that generally matches andmates with the topography of an anterior portion of a femur that isexposed as part of a total hip arthroplasty procedure. Opposite the bonecontacting surface 214 is a stem interfacing surface 216 that, inexemplary form, is planar. A series of holes 220-224 extend through thefemoral bone base plate 200 from the bone contacting surface 214 to thestem interfacing surface 216. In this exemplary embodiment, the femoralbone base plate 200 includes three holes 220 configured to receive screwfasteners (not shown) to mount the base plate 200 to the femur 204. Inexemplary fashion, each hole 220 includes a recessed collar 226 that isoperative to change the cylindrical diameter of each hole so that thehole at the stem interfacing surface 216 has a larger diameter than thehole at the bone contacting surface 214. Two additional holes 222 areprovided that receive alignment studs associated with the stem 206. Afastener hole 224 is also provided, which may include helical threads,that is configured to receive a fastener in order to retain the femoralbone base plate into engagement with the stem 206.

Referring to FIGS. 14-19 , the exemplary stem 206 includes a distaladapter 230 having a pair of alignment studs 232 extending therefromthat are configured to be received within respective holes 222 of thefemoral bone base plate 200. In exemplary form, each alignment stud 232comprises a linear, cylindrical shape that is received within acylindrical bore of the respective holes 222. At the same time, thedistal adapter 230 includes a through hole 234 of its own that isconfigured to receive a fastener 250 (such as the locking screw of FIG.18 , which may be threaded 252) to mount the distal adapter to thefemoral bone base plate 200. In this exemplary embodiment, the distaladapter 230 includes a series of interconnected arcuate cut-outs 236that unobstruct the holes 220 of the femoral bone base plate 200.Extending proximally from the distal adapter 230 is an elongated neck240 terminating at a proximal coupling 242 configured to engage the IMU202. The stem 206 is angled in three dimensions so that it can extendthrough a typical anterior THA incision before and after externalrotation of the femur. The stem 206 has two configurations to accept theIMU 202. The first configuration of the stem 206 features a coupling 242to accept the locking feature of the IMU 202. The second configurationof the stem 206 features a slide on which an IMU 202 is mounted.

Referring to FIGS. 20 and 21 , attachment of the stem 206 to the femoralbone base plate 200 includes aligning the studs 232 of the stem with therespective holes 222 of the base plate. By way of example, the studs 232are designed to fit snugly with respect to the hole 222 boundaries toavoid significant play between the stem 206 and base plate 200. Afterthe studs 232 are received within the holes 222, the through hole 234 ofthe adapter 230 should be aligned with the hole 224 of the base plate200 so that the fastener 250 can extend through the smooth bore hole 234and its threads 252 can engage the protruding threads of the hole 224.In this fashion, as the fastener 250 is rotated clockwise, the head ofthe fastener is operative to sandwich the adapter 230 in between thebase plate 200. Upon proper torquing of the fastener 250, the stem 206and the base plate 200 are fixedly mounted to one another. After beingmounted to one another, the holes 222 of the base plate are available tobe accessed by a drill and thereafter by a screw to mount the assembly210 to the femur 204, presuming the IMU 202 is mounted to the stem 206.

When mounting the assembly 210 to a femur, the assembly is placed on theanterior of the proximal femur along the intertrochanteric line andperpendicular to the femoral neck axis during anterior total hiparthroplasty. It may be secured to the anterior femur with three 3.5millimeter×20 millimeter cancellous screws (not shown). In this fashion,the reference IMU 202 is securely fixed to the patient femur.

Referring to FIGS. 22 and 23 , an alternate exemplary embodiment of abone reference assembly 310 for a femur 304 comprises an inertialmeasurement unit 302, a stem 306, and a bone base plate 300 (inexemplary form, a femoral bone base plate). Though not necessarilylimited to applications on an attachment site on the posterior region ofthe femur, the foregoing exemplary embodiment may be referred to as anexemplary posterior bone reference assembly 310.

As depicted in more detail in FIGS. 24-26 , the shape of the exemplaryfemoral bone base plate 300 and fixation locations are establishedmathematically and confirmed using bone models 100 from a statisticalatlas. The exemplary femoral bone base plate 300 includes a distal, bonecontacting surface 314 having a topography that generally matches andmates with the topography of a posterior portion of a femur that isexposed as part of a total hip arthroplasty procedure. Opposite the bonecontacting surface 314 is a stem interfacing surface 316 that, inexemplary form, is planar. A series of holes 320-324 extend through thefemoral bone base plate 300 from the bone contacting surface 314 to thestem interfacing surface 316. In this exemplary embodiment, the femoralbone base plate 300 includes three holes 320 configured to receive screwfasteners (not shown) to mount the base plate 300 to the femur 304. Inexemplary fashion, each hole 320 includes a recessed collar 326 that isoperative to change the cylindrical diameter of each hole so that thehole at the stem interfacing surface 316 has a larger diameter than thehole at the bone contacting surface 314. Two additional holes 322 areprovided that receive alignment studs associated with the stem 306. Afastener hole 324 is also provided, which may include helical threads,that is configured to receive a fastener in order to retain the femoralbone base plate into engagement with the stem 306.

Referring to FIGS. 27 and 28 , the exemplary stem 306 includes a distaladapter 330 having a pair of alignment studs 332 extending therefromthat are configured to be received within respective holes 322 of thefemoral bone base plate 300. In exemplary form, each alignment stud 332comprises a linear, cylindrical shape that is received within acylindrical bore of the respective holes 322. At the same time, thedistal adapter 330 includes a through hole 334 of its own that isconfigured to receive a fastener 350 (such as the locking screw of FIG.29 , which may be threaded 352) to mount the distal adapter to thefemoral bone base plate 300. In this exemplary embodiment, the distaladapter 330 includes a pair of arcuate cut-outs 336 that unobstruct theholes 320 of the femoral bone base plate 300. Extending proximally fromthe distal adapter 330 is an elongated neck 340 terminating at aproximal coupling 342 configured to engage the IMU 302. The stem 306 isangled in three dimensions so that it can extend through a typicalposterior THA incision before and after external rotation of the femur.The stem 306 has two configurations to accept the IMU 302. The firstconfiguration of the stem 306 features a coupling 342 to accept thelocking feature of the IMU 302. The second configuration of the stem 306features a slide on which an IMU 302 is mounted.

Referring to FIGS. 30-33 , attachment of the stem 306 to the femoralbone base plate 300 includes aligning the studs 332 of the stem with therespective holes 322 of the base plate. By way of example, the studs 332are designed to fit snugly with respect to the hole 322 boundaries toavoid significant play between the stem 306 and base plate 300. Afterthe studs 332 are received within the holes 322, the through hole 334 ofthe adapter 330 should be aligned with the hole 324 of the base plate300 so that the fastener 350 can extend through the smooth bore hole 334and its threads 352 can engage the protruding threads of the hole 324.In this fashion, as the fastener 350 is rotated clockwise, the head ofthe fastener is operative to sandwich the adapter 330 in between thebase plate 300. Upon proper torquing of the fastener 350, the stem 306and the base plate 300 are fixedly mounted to one another. After beingmounted to one another, the holes 322 of the base plate are available tobe accessed by a drill and thereafter by a screw to mount the assembly310 to the femur 304, presuming the IMU 302 is mounted to the stem 306.

When mounting the assembly 310 to a femur, the assembly is placed on theposterior of the proximal femur along the intertrochanteric line andperpendicular to the femoral neck axis during posterior total hiparthroplasty. It may be secured to the posterior femur with three 3.5millimeter×20 millimeter cancellous screws (not shown). In this fashion,the reference IMU 302 is securely fixed to the patient femur.

Following from the above description, it should be apparent to those ofordinary skill in the art that, while the methods and apparatuses hereindescribed constitute exemplary embodiments of the present disclosure,the invention is not limited to these precise embodiments and thatchanges may be made to such embodiments without departing from the scopeof the invention as defined by the claims. Additionally, it is to beunderstood that the invention is defined by the claims and it is notintended that any limitations or elements describing the exemplaryembodiments set forth herein are to be incorporated into theinterpretation of any claim element unless such limitation or element isexplicitly stated. Likewise, it is to be understood that it is notnecessary to meet any or all of the identified advantages or objects ofthe invention disclosed herein in order to fall within the scope of anyclaims, since the invention is defined by the claims and since inherentand/or unforeseen advantages of the present invention may exist eventhough they may not have been explicitly discussed herein.

What is claimed is:
 1. A femoral base plate assembly comprising: a platecomprising a bone contacting surface configured to receive an exteriorof a femur, and a top surface opposite the bone contacting surface, afirst plurality of orifices configured to receive respective fasteners,each of the first plurality of orifices extending through the bonecontacting surface and through the top surface, and a second pluralityof orifices with at least one of the second plurality of orifices beingthreaded; and a stem removably mounted to the plate and comprising aneck having a distal end adjacent the top surface of the plate, and aproximal end spaced from the distal end and extending away from thefemur, an inertial measurement unit mounted to the proximal end of theneck, and a distal adapter coupled to the distal end of the neck andcomprising a body, and a plurality of studs extending distally therefromto be received within the second plurality of orifices, the distaladapter not covering the first plurality of orifices when the stem ismounted to the plate so that the respective fasteners can be received bythe first plurality of orifices.
 2. The femoral base plate assembly ofclaim 1, wherein at least one of the first plurality of orificesincludes a collar recessed with respect to the top surface and the bonecontacting surface.
 3. The femoral base plate assembly of claim 1,wherein the first plurality of orifices is arranged in a triangularconfiguration.
 4. The femoral base plate assembly of claim 1, whereinthe first plurality of orifices is arranged along a straight line. 5.The femoral base plate assembly of claim 1, wherein a longitudinal axisof each of the first plurality of orifices is non-parallel to oneanother.
 6. The femoral base plate assembly of claim 1, wherein at leastone of the second plurality of orifices includes a uniform longitudinalcross-section.
 7. The femoral base plate assembly of claim 1, wherein atleast one of the second plurality of orifices includes a non-uniformlongitudinal cross-section.
 8. The femoral base plate assembly of claim1, wherein each of the second plurality of orifices includes a uniformlongitudinal cross-section.
 9. The femoral base plate assembly of claim1, wherein the second plurality of orifices is arranged in a straightline.
 10. The femoral base plate assembly of claim 1, wherein the secondplurality of orifices is arranged in a triangular configuration.
 11. Thefemoral base plate assembly of claim 1, wherein a longitudinal axis ofeach of the plurality of second orifices is parallel to one another. 12.The femoral base plate assembly of claim 1, wherein a longitudinal axisof each of the plurality of second orifices is not parallel to oneanother.
 13. The femoral base plate assembly of claim 1, wherein aspatial relationship between the inertial measurement unit and the plateis constant.
 14. The femoral base plate assembly of claim 1, wherein theplate comprises a projection extending from the top surface; and whereinthe distal adapter includes an orifice configured to receive theprojection of the plate.
 15. The femoral base plate assembly of claim 1,wherein each of the plurality of studs comprises a linear stud.
 16. Afemoral base plate assembly comprising: a plate comprising a bonecontacting surface configured to receive an exterior of a femur, and atop surface opposite the bone contacting surface, a plurality oforifices configured to receive respective fasteners, each of theplurality of orifices extending through the bone contacting surface andthrough the top surface opposite the bone contacting surface, and aplurality of cavities on the top surface adjacent the plurality oforifices; a stem removably mounted to the plate and comprising a neckhaving a distal end adjacent the top surface of the plate, and aproximal end spaced from the distal end and extending away from thefemur, a distal adapter coupled to the distal end of the neck andcomprising a body with a plate mounting surface opposite the neck andconfigured to receive the top surface of the plate, and a plurality ofstuds extending distally from the plate mounting surface, an inertialmeasurement unit mounted to the proximal end of the neck, and theplurality of studs cooperating with the plate to be received within theplurality of cavities so as to align the stem with respect to the platewhen the stem is removably mounted to the plate, the distal adapter notcovering the plurality of orifices when the stem is mounted to the plateso that the respective fasteners can be received by the plurality oforifices.
 17. The femoral base plate assembly of claim 16, wherein atleast one of the plurality of orifices includes a collar recessed withrespect to the top surface and the bone contacting surface.
 18. Thefemoral base plate assembly of claim 16, wherein the plurality oforifices is arranged in a triangular configuration.
 19. The femoral baseplate assembly of claim 16, wherein each of the plurality of studscomprises a linear stud.
 20. The femoral base plate assembly of claim16, wherein each of the plurality of studs comprises a cylinder-shapedstud extending distally from and perpendicular to the plate mountingsurface.